Written by Olivia Hunt
19th Apr 2023 • 7 minute read
Dr Nadja Auerbach
Reviewed by
Dr Nadja Auerbach, MBBS BSc Dip IBLM/BSLM

Every month, your body goes through a series of hormonal changes resulting in pregnancy or a period — this is called your menstrual cycle. Learn about the different phases of your cycle, the critical hormones involved, and what to do if you notice any changes. 

What’s the menstrual cycle?

The menstrual cycle is the time from the first day of your period to the day before your next period

In the first half of your cycle, your body helps prepare the releasing of an egg from the ovaries and develop a new womb lining after your last period. Your hormones help prepare your womb for pregnancy in the second half of your cycle.  If you don’t get pregnant, a period is triggered, which marks the start of another cycle. 

Get insights into the hormones involved in your menstrual cycle by doing a women’s hormones blood test.

What’s the average menstrual cycle length?

The average menstrual cycle can be anything from 23 to 35 days — it’s important to remember every woman is different. 

You can use many useful apps to track your menstrual cycle and associated symptoms or conditions — like PMS, endometriosis, and premenstrual dysphoric disorder.  

If you’re concerned about irregular periods or notice other changes to your menstrual cycle, you should speak to your GP.

When does the menstrual cycle start? 

Your periods typically start around age 12. But some girls will start them earlier or later. 

Starting your period later isn’t usually a cause for concern. Most girls have regular periods from age 16 to 18. 

When do you stop having a menstrual cycle?

Unless you get pregnant, you’ll have menstrual cycles until menopause. Your menstrual cycle stops when you reach menopause

Menopause is when you have stopped having periods for one year. This means you can no longer get pregnant naturally. Typically, women transition into menopause between ages 45 and 55 (the UK average is age 51). Sometimes this can happen below the age of 40 — early menopause.

Learn about your menopausal health with our menopause insights blood test.

What are the menstrual cycle phases?

The menstrual cycle has three distinct phases — the follicular phase, ovulation, and the luteal phase.   

Follicular phase

The follicular phase prepares your body for ovulation. It starts on the first day of your period and lasts 10 to 16 days. This can vary from cycle to cycle. 

High FSH levels stimulate the growth and maturation of follicles — sacs in your ovaries containing immature eggs. 

As your follicles grow, they produce oestrogen. Many follicles grow at the beginning of your cycle until a dominant follicle emerges.

Increased oestrogen and low progesterone might improve your skin’s appearance in this phase. An improved mood is also associated with this phase.  

Once there’s enough oestrogen in your body, the next phase of the menstrual cycle begins.


Ovulation is when one of your ovaries releases a mature egg. It happens when high oestrogen levels trigger your brain to release luteinising hormone (LH). This surge in LH is what triggers ovulation. 

Ovulation typically happens 12 to 16 days before your next period starts — but this varies from woman to woman. 

During ovulation, a mature egg travels down your fallopian tube towards the womb (uterus), ready for fertilisation by sperm.  

If you track your cycle, many symptoms can signify ovulation is close to occurring. These include. 

  • changes to your discharge — it might develop an egg-white consistency
  • feeling hotter than usual
  • an increased sex drive 
  • ovulation pain — sometimes strenuous exercise can trigger this
  • breast tenderness

You might experience all these symptoms, just a few, or none at all. And these might differ each month.

Luteal phase 

The luteal phase begins following ovulation. 

The empty follicle left behind becomes a corpus luteum — a completely normal cyst that forms on your ovary every month. This is what produces the hormone progesterone.  

Progesterone is essential for preparing a thick uterine lining to implant a fertilised egg (embryo). If egg fertilisation happens and you become pregnant, the corpus luteum grows and produces progesterone until the placenta can take over. Progesterone levels continue increasing to sustain a pregnancy and support embryo development. 

If you don’t become pregnant, your corpus luteum shrinks, causing oestrogen and progesterone levels to fall. Once your progesterone levels become extremely low, your uterus lining starts to shed, marking the beginning of your period. 

Towards the end of the luteal phase, you might experience the following:

  • bloating
  • cramps
  • tiredness
  • breast tenderness
  • food cravings
  • changes to your mood 

During the days leading up to your period, you might consider activities that relax your body, like yoga or pilates, to help relieve cramps and muscle fatigue. But don’t be afraid to rest if you don’t feel like being overly active during this time. 

It’s also important to stay hydrated by drinking plenty of water and eating healthy snacks and well-balanced meals. Before your period, you should avoid consuming excessive saturated fats, refined sugars, and processed food. While you might have cravings for these in the short term, they can affect your hormones and make you feel more tired.


Menstruation is also called a period. This is when your body sheds the lining of your uterus (womb). 

Menstrual blood and tissue leave your body through your vagina. A period typically lasts from two to seven days. 

The length of your periods might differ monthly depending on your stress levels, any hormonal contraception you’re taking, and conditions like PCOS.

Some women's periods can be heavy, while others might be light. This can also change from month to month. 

When menstruation begins, this signifies the end of your last cycle and the start of a new one. 

How to manage painful periods

Many women experience pain during periods. Self-help remedies are usually enough to manage it at home.

You could try:

  • anti-inflammatory medication — like ibuprofen
  • stopping smoking — this might increase your risk of period pain
  • exercise — gentle swimming, walking, or cycling might help reduce pain even if you don’t feel like being active
  • heat — putting a hot water bottle (wrapped in a tea towel) on your tummy might help reduce pain
  • warm bath or shower — this can relieve pain and help you relax
  • massage — light, circular massage around your lower tummy may help reduce pain
  • yoga or pilates — these might help distract you from feelings of pain and discomfort
  • transcutaneous electronic nerve stimulation (TENS) — a small battery-operated device that sends a mild electrical current to your tummy to help reduce pain
  • magnesium supplements — can reduce negative thoughts, bloating, stress, and other symptoms of PMS
  • omega-3 supplements — studies show omega-3 can help reduce period pain

You should see your GP if the advice above doesn’t help. They might prescribe a stronger painkiller, like naproxen or codeine. 

Sometimes, painful periods can indicate conditions like endometriosis or PCOS. It’s also important to remember that extreme period pain isn’t something you should put up with — make sure you get your symptoms checked out to find something that works for you.  

Changes to your cycle are usually nothing to worry about. 

But you should see your doctor if:

  • you bleed between your periods, after sex, or after menopause
  • the number of days in between your period keep changing
  • your periods are closer together or further apart than usual
  • you’re finding it difficult to get pregnant after one year of trying to conceive

Tracking your cycle using an app or diary is a helpful way to understand your cycle better. You can work out what’s normal for you and identify how hormonal changes can make you feel throughout the month. 

Tracking can also help you determine if there are any sudden changes to your cycle length. 

Why can your menstrual cycle become longer or shorter?

Changes to your menstrual cycle aren't always a problem, but knowing what’s normal for you and identifying if something is causing irregular periods can be helpful. 

You might experience changes to your periods due to: 

  • perimenopause or menopause — your hormone levels start to fluctuate 
  • pregnancy — a missed period is usually the first sign
  • extreme weight loss, exercise, or stress — all three can cause your periods to become irregular or stop completely
  • the contraceptive pill — withdrawal bleeding might become lighter 

Periods can also sometimes stop due to medical conditions. These include: 

If you’re concerned about the length or frequency of your periods, you should speak to a healthcare professional to understand the possible causes.